This application is based upon and claims priority of Japanese Patent Application No. 2001-272291, filed on Sep. 7, 2001, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a reticle, and a pattern positional accuracy measurement device and method and, more particularly, to a reticle required to have high positional accuracy in, e.g., an edge portion of a device pattern, and a device and method of measuring the pattern positional accuracy of the reticle.
2. Description of the Related Art
In the fabrication processes of devices such as semiconductor devices (including LSIs), magnetic devices, liquid crystal devices, and printed circuit boards, a reticle having device patterns to be transferred is used to transfer the device patterns onto (to expose) a semiconductor wafer (to be also simply referred to as a xe2x80x9cwaferxe2x80x9d hereinafter).
FIG. 5A is a view showing a reticle having device patterns formed on it.
Referring to FIG. 5A, a reticle 50 has, e.g., a glass plate as its substrate, and a plurality of device patterns 52 to be transferred are repeatedly formed at intervals in a device region 51 of this substrate. These device patterns 52 are formed by, e.g., chromium which functions as a light-shielding film during exposure.
A method of fabricating this reticle 50 will be explained below. First, a chromium layer is formed on a glass substrate. In the fabrication of the reticle 50 described above, a resist portion of the substrate coated with the resist is irradiated with an electron beam (EB) or a laser in accordance with the shape of the device patterns 52. After that, an unnecessary resist is removed by development. In addition, the residual resist is used as a mask to perform etching, thereby forming the device patterns 52 by chromium on the substrate.
FIG. 5B is a view showing device patterns 55 transferred onto a semiconductor wafer 53 by using the reticle 50 shown in FIG. 5A. As shown in FIG. 5B, the device patterns 55 having the same shape as the device patterns 52 formed at intervals in the device region 51 of the reticle 50 are transferred onto the wafer 53.
FIGS. 5C and 5D are enlarged views of a portion 54 having a plurality of transferred device patterns shown in FIG. 5B.
That is, FIG. 5C shows the device patterns 55 transferred onto the wafer 53 by using the reticle 50 in which no deviation occurs in the arrangement in the row direction of the device patterns 52. As shown in FIG. 5C, no deviation from a dotted line Y51 occurs in the arrangement in the row direction of the device patterns 55 transferred onto the wafer 53.
On the other hand, FIG. 5D shows the device patterns 55 transferred onto the wafer 53 by using the reticle 50 in which deviation occurs in the arrangement in the row direction of the device patterns 52. In this case, as shown in FIG. 5D, deviation having a distance L51 from the dotted line Y51 occurs in the arrangement in the row direction of the device patterns 55 transferred onto the wafer 53.
This deviation occurring in the arrangement of the device patterns 55 transferred onto the wafer 53 by the deviation in the arrangement of the device patterns 52 of the reticle 50 causes variations in the performance of the fabricated devices. In the fabrication of a reticle, therefore, the positional accuracy of the device patterns 52 on the reticle is measured to check whether the required positional accuracy is met, i.e., whether deviation has occurred in the arrangement of the device patterns 52.
A method of measuring the positional accuracy of device patterns on a conventional reticle will be explained with reference to FIGS. 6 and 7.
FIG. 6 is a view showing a method of arranging positional accuracy measurement patterns for measuring the positional accuracy of device patterns on a conventional reticle. As shown in FIG. 6, cross-shaped positional accuracy measurement patterns 61 are evenly arranged in positions fixed regardless of layers in the perimeter outside a device region 51 of a reticle 50. xe2x80x9cLayersxe2x80x9d mean the layers of each device formed on a wafer.
To measure the positional accuracy of device patterns on the reticle, as shown in FIG. 7, each of the cross-shaped positional accuracy measurement patterns 61 arranged as above is scanned in an X direction 71 and a Y direction 72, thereby acquiring X-coordinates X71 and X72 and Y-coordinates Y71 and Y72. In addition, the position of a pattern center CP2 is calculated on the basis of the X-coordinates X71 and X72 and the Y-coordinates Y71 and Y72. More specifically, the X-coordinate of the pattern center CP2 is calculated by (X71+X72)/2, and the Y-coordinate of the pattern center CP2 is calculated by (Y71+Y72)/2.
The position of the pattern center CP2 calculated as above is compared with the central position of a positional accuracy measurement pattern based on the design value of the reticle. In this manner, the positional accuracy of device patterns on the reticle is measured and evaluated.
In the above method of measuring the positional accuracy of device patterns on a reticle, however, the positional accuracy of device patterns is measured and evaluated on the basis of the position of the pattern center of each positional accuracy measurement pattern formed. Therefore, even if the formed positional accuracy measurement pattern evenly becomes thick or thin, it does not change the center position of the positional accuracy measurement pattern, and the measurement result of the positional accuracy of device patterns is thus to be xc2x10. That is, it is determined that no deviation has occurred in the arrangement of device patterns.
Assume, for example, that a cross-shaped positional accuracy measurement pattern 81 having a design value Ld81 as a width as shown in FIG. 8A is to be formed. If, as shown in FIG. 8B, the pattern dimensions increase (the pattern becomes thick) symmetrically with respect to central lines in the X and Y directions of this positional accuracy measurement pattern 81, and if a positional accuracy measurement pattern 82 having a width Ly81 is formed, pattern centers CP3 and CP4 of these positional accuracy measurement patterns 81 and 82 are in the same position because the pattern dimensions increase symmetrically with respect to the central lines in the X and Y directions.
Analogously, as shown in FIG. 8C, if the pattern dimensions decrease (the pattern becomes thin) symmetrically with respect to the central lines in the X and Y directions of this positional accuracy measurement pattern 81, and if a positional accuracy measurement pattern 83 having a width Ly82 is formed, pattern centers CP3 and CP5 of these positional accuracy measurement patterns 81 and 83 are in the same position because the pattern dimensions decrease symmetrically with respect to the central lines in the X and Y directions.
Also, in the recent reticle fabrication, reticles are beginning to be required to have high device pattern positional accuracy, high pattern size accuracy, and the like, with the advancing downsizing and increasing storage capacity of devices, Accordingly, the positional accuracy and the like must be measured more accurately to guarantee the quality of reticles.
Additionally, the positional accuracy of device patterns on the conventional reticle is ensured on the basis of the pattern center of a measured positional accuracy measurement pattern. In a device such as a magnetic device, for example, high positional accuracy is sometimes required in an edge portion of a device pattern which is different from the pattern central position of a positional accuracy measurement pattern.
FIG. 9 is a view for explaining the relationship between the positional accuracy of a positional accuracy measurement pattern on the conventional reticle and the positional accuracy of device patterns of magnetic devices (MR heads: magnetoresistance heads).
That is, FIG. 9 shows an example in which patterns actually formed on a reticle are larger than their design values. Referring to FIG. 9, a positional accuracy measurement pattern 91 and device patterns 92 and 93, indicated by the dotted lines, are patterns based on design values. A positional accuracy measurement pattern 94 and device patterns 95 and 96, indicated by the solid lines, are patterns actually formed on the reticle. Also, in the device patterns 95 and 96 of MR heads shown in FIG. 9, high positional accuracy is required in the Y-coordinates of pattern edge portions P91 and P92, in order to prevent variations in the performance of these MR heads.
As shown in FIG. 9, assume that the positional accuracy measurement pattern 94 having a width Ly91 is formed, which is one size larger in every direction from a pattern center CP6 than the positional accuracy measurement pattern 91 having a designed width Ld91. In this case, the pattern dimensions of the actually formed positional accuracy measurement pattern 94 increase symmetrically with respect to central lines extending in the X and Y directions of the designed positional accuracy measurement pattern 91. So, both the pattern centers of these positional accuracy measurement patterns 91 and 94 are the point CP6. Accordingly, the measurement result of the device pattern positional accuracy on this reticle is xc2x10, i.e., it is determined that no difference from the design value is produced.
The Y-coordinates of the pattern edge portions P91 and P92, however, where high positional accuracy is required in the device patterns 95 and 96, produce a difference of a length H2 (=(Ly91xe2x88x92Ld91)/2) from the designed Y-coordinate. For example, if the design value Ld91 of the positional accuracy measurement pattern is 10 xcexcm and the actual width Ly91 is 12 xcexcm, the pattern edge portions P91 and P92 of the device patterns 95 and 96 produce a difference of H2=1 xcexcm from the designed position.
If a portion required to have high positional accuracy changes in accordance with device patterns on a reticle as described above, the conventional device pattern positional accuracy measurement method cannot accurately measure the positional accuracy of a portion required to have high positional accuracy. Accordingly, the conventional device pattern positional accuracy measurement method may determine that there is no deviation in the arrangement of device patterns on a reticle, even if arrangement deviation occurs in an arbitrary portion required to have high positional accuracy in a device pattern, e.g., in an edge portion of the device pattern. Consequently, the required device pattern positional accuracy of a reticle cannot be met.
The present invention has been made to solve the above conventional problem, and has as its object to accurately measure the positional accuracy of an arbitrary portion required to have high positional accuracy in a device pattern formed on a reticle.
In a reticle of the present invention, a positional accuracy measurement pattern for evaluating the positional accuracy of a device pattern formed in a device region is so formed that the position of a portion required to have high positional accuracy in the device pattern and the central position of the positional accuracy measurement pattern are present on the same straight line perpendicular to a direction in which the high positional accuracy is necessary.
In the reticle of the present invention constructed as above, the device pattern and the positional accuracy measurement pattern are so formed that the position of a portion required to have high accuracy in the device pattern and the central position of the positional accuracy measurement pattern are arranged on the same straight line in accordance with a direction in which the high positional accuracy is necessary. Therefore, the positional accuracy of the portion where the high positional accuracy is required in the device pattern can be evaluated from the actually measured central position of the positional accuracy measurement pattern.
A pattern positional accuracy measurement device of the present invention comprises a positional information detector for detecting positional information of a pattern formed on a reticle, an arithmetic unit for calculating the pattern central position and pattern dimension of the pattern on the basis of the positional information, and calculating the positional accuracy of a portion required to have high positional accuracy in a device pattern formed on the reticle, and an output unit for outputting the positional accuracy of the device pattern.
In the pattern positional accuracy measurement device of the present invention constructed as above, the pattern central position and pattern dimension of a pattern for calculating the positional accuracy of a device pattern are calculated on the basis of the detected positional information, thereby calculating the positional accuracy of the device pattern. Therefore, the positional accuracy of the device pattern can be calculated by taking account not only of the pattern central position of the pattern for calculating positional accuracy but also of a dimensional accuracy component of the pattern dimension with respect to a design value.